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Background <p>Proton therapy offers precise dose delivery while minimizing damage to surrounding healthy tissues. However, concerns persist regarding skin toxicity due to energy dispersion beyond the Bragg peak. Accurate surface dose measurement is critical for evaluating patient radiation exposure, though existing methods are often complex and imprecise.</p> Purpose <p>This study aims to determine surface dose correction factors (Scf) for various detectors in spot scanning proton therapy and to analyze the impact of clinical parameters on surface dose.</p> Methods <p>Surface doses were measured in a water phantom using PTW Advanced Markus, PTW Roos chamber, and IBA FC65-G Farmer chamber, normalized at a 3&#xa0;cm depth. Experimental results were compared with FLUKA Monte Carlo simulations, normalized at 70&#xa0;µm, to calculate Scf. Additional evaluations were conducted using Eclipse. The effects of proton beam energy (100, 150, and 200&#xa0;MeV), air gap distances (5&#xa0;cm, 15&#xa0;cm, and snout position at 42.1&#xa0;cm), and range shifter (RS) thicknesses (2&#xa0;cm, 3&#xa0;cm, and 5&#xa0;cm) on surface dose were assessed.</p> Results <p>The Scf values for the Advanced Markus, Roos, and FC65-G detectors were 0.9839, 0.9362, and 0.9701, respectively, with variations under 1% across energies. Surface dose decreased with increasing air gap distance, while the introduction of an RS increased surface dose, particularly with reduced air gaps and thicker RS.</p> Conclusions <p>The derived correction factors improve surface dose measurement accuracy in proton pencil beam scanning. RS presence notably increases surface dose, particularly at air gaps below 5&#xa0;cm, with an average rise of 6%.</p>

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Determination of the surface dose correction factors for various detectors in proton scanning therapy

  • 期刊论文

  • 发表日期：

    2025年11月3日

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  • Pakjira Saruang,
  • Taweap Sanghangthum,
  • Mintra Keawsamur

摘要

Background

Proton therapy offers precise dose delivery while minimizing damage to surrounding healthy tissues. However, concerns persist regarding skin toxicity due to energy dispersion beyond the Bragg peak. Accurate surface dose measurement is critical for evaluating patient radiation exposure, though existing methods are often complex and imprecise.

Purpose

This study aims to determine surface dose correction factors (Scf) for various detectors in spot scanning proton therapy and to analyze the impact of clinical parameters on surface dose.

Methods

Surface doses were measured in a water phantom using PTW Advanced Markus, PTW Roos chamber, and IBA FC65-G Farmer chamber, normalized at a 3 cm depth. Experimental results were compared with FLUKA Monte Carlo simulations, normalized at 70 µm, to calculate Scf. Additional evaluations were conducted using Eclipse. The effects of proton beam energy (100, 150, and 200 MeV), air gap distances (5 cm, 15 cm, and snout position at 42.1 cm), and range shifter (RS) thicknesses (2 cm, 3 cm, and 5 cm) on surface dose were assessed.

Results

The Scf values for the Advanced Markus, Roos, and FC65-G detectors were 0.9839, 0.9362, and 0.9701, respectively, with variations under 1% across energies. Surface dose decreased with increasing air gap distance, while the introduction of an RS increased surface dose, particularly with reduced air gaps and thicker RS.

Conclusions

The derived correction factors improve surface dose measurement accuracy in proton pencil beam scanning. RS presence notably increases surface dose, particularly at air gaps below 5 cm, with an average rise of 6%.